Document Preview

Publisher Society of Exploration Geophysicists Language English

Document ID 2010-0096

Content Type Conference Paper

Title Long Sweep Times Increase the Recoverable Higher Frequencies For Mid-continentSeismic Data

Authors Bruce Karr*, Fairfieldnodal; Robert A.Hefner IV, BEREXCO LLC

Source 2010 SEG Annual Meeting, October 17 - 22, 2010 , Denver, Colorado

Copyright 2010. Society of Exploration Geophysicists

Preview Summary

Fewer long vibroseis sweep times with short tapers have increased the dynamic range compared to stacking many

shorter sweeps. Recent testing in the field has shown that when the total sweep energy is taken into account that

fewer longer sweep times do a better job at putting more recoverable higher frequencies in the ground. For much of

the mid-continent a typical sourcing for a 3D survey would be eight 10 second sweeps or approximately 80 seconds

of total sweep energy. After sweep testing 31 project start-ups in Kansas, Nebraska and Oklahoma, using two 40

second sweeps compared to eight 10 second sweeps as increased the dynamic range of interpretable migrated

seismic data. The purpose of our testing was to improve frequencies from 50 to 100+ Hz. While parts of the

mid-continent are known for good recoverable frequency as high as 100Hz, several areas struggle to get over 50Hz.

The longer sweeps increased the higher frequencies in all areas.

INTRODUCTION

A standard mid-continent source effort for the last decade is two vibs shaking eight 10 second sweeps over 16-120

hertz, at an increasing rate of 3db/oct and applying a 500msec taper to both the start and end of the sweep. While

the number of sweeps fluctuated between 6 and 10, and the sweep lengths ranged from 8 to 12 seconds, the

outcome was very similar in the final migrated products. This project started and continues to try and increase the

dynamic range. The goal is to test every project at the start-up for the best start frequency which doesnt over drive

the noise and signal for the lower frequencies of 6-30 hertz and predict the highest recoverable frequency from a set

of vibroseis field test records. The ability to email or FTP field test records to a processing center with a complete

suite of processing tools has helped us select the best set of sweep parameters in real time. Looking at a

geographic swath across Nebraska, Central Kansas and the Panhandle of Oklahoma, similar flat geology is seen

producing different dynamic ranges in typical seismic data. (Figure 1 & 2) The near surface weathering zone

and its thickness are believed to be the main controlling factors in what frequencies are recoverable. The Kansas

central uplift has the thinnest weathering zone with the best high frequencies being recovered. While the

southwestern Kansas, the Panhandle of Oklahoma and southeastern Colorado have a very thick weathering zone

and struggle to get frequencies above 60 hertz. Due to this variability in dynamic range absorption across this

region, we test every project for the optimal set of sweep parameters. Typically we design 14 - 18 sweep tests to be

done during the layout at the beginning of every 3D survey. These tests are then emailed from the field to a

processing center. Once in a processing shop a full set of processing tools can be used to evaluate noise, signal and

dynamic range. Every project is unique in selecting the right set of tools.

File Size 659 KB Number of Pages 5

Add to Cart

0 itemsCheckout

PRICEPRICE

US $ 21.00

Change Currency

DOWNLOAD HISTORYDOWNLOAD HISTORY

Past 30 days -0 times

Since 2007 - 5 times

ABOUT ONEPETROABOUT ONEPETRO

What is OnePetro

Top Downloads

Document Coverage

Participating Organizations

Subscription Options

Login Help

Administrator Access

LATEST NEWSLATEST NEWS

Have you visited PetroWiki?

IMPORTANT NOTE

Download accelerators and bots of any

kind are prohibited on this website.

Offenders may have their access

blocked.

187.195.203.217 Privacy Policy powered by SPE.org

Home Login Contact Us Help

View Cart

Long Sweep Times Increase the Recoverable Higher Frequencies For Mi... http://www.onepetro.org/mslib/servlet/onepetropreview?id=SEG-2010-0096

1 of 1 11/29/2013 1:33 PM